Independent and Combined Effects of Arterial Angulations and Shear Stress on Vascular Function

Abstract

Excessive sedentary time is a significant health risk, independent of daily physical activity or exercise. In particular, long periods of prolonged sitting is associated with an increased risk of cardiovascular disease. Prolonged sitting reduces flow-mediated dilation (FMD), which is a key indicator of vascular health. Recent evidence suggests that the seated position strains the arteries through angulations that create turbulent blood flow, thereby reducing FMD. However, when blood flow in the arteries is slightly increased (via local heating), vascular function improves even when seated. However, the combined effects of removing arterial angulations (i.e., standing) and increasing shear stress (i.e., local heating) on reducing sitting-induced vascular dysfunction have yet to be investigated. PURPOSE: This project aims to determine if arterial angulations (through sitting or standing), shear stress (through local heating), or a combination of these factors affect vascular function. METHODS: 13 individuals (n = 4 male; n = 9 female) participated in a randomized crossover design study. Participants completed two experimental trials (one sitting and one standing). At the beginning of each experimental trial, participants laid supine for at least 20-minutes prior to baseline measurements of FMD at the superficial femoral artery (SFA). Participants then moved into a sitting or standing position. One leg was then passively heated through a water-perfused pant leg in order to increase shear rate. Participants maintained this position for 2-h. Participants then returned to a supine position and post measures of FMD were obtained. RESULTS: Overall, sitting led to approximately a 1.2% decline in FMD. Standing appeared to confer the greatest benefit independent of heating (p = .025) . By the end of standing, participants FMD was 2.88% (p = .037) greater than after 2-h of sitting. However, there was no significant effect of local heating (0.75 % ± 1.90, p = .594) and no interaction between heating and body position (-0.17 % ± 2.70, p = .879). CONCLUSION: Standing was superior to sitting with regards to FMD while local heating had a non-significant effect. However, future studies need to examine modifiers such as biological sex.